594 LIFE ' OUTLINES OF GENERAL BIOLOGY 



some clearly conceived purpose or ideal; or there is an expression 

 of an abstract idea in significant artistic form. Whatever definition 

 be used there is general demarcation of rational conduct, as dis- 

 tinguished from intelligent behaviour. So far as is known, this 

 higher level is not definitely reached by any animal; though, as we 

 shall see, there are adumbrations of reason in the higher apes. 



(la) SUBCONSCIOUS THINKING.— Those disciplined in pro- 

 longed and resolute thinking at a high level often acquire great 

 expertness. Habituation in rational and abstract discourse is familiar 

 to the mathematician and the philosopher; and there comes to be 

 an enregistration of the habit of experimenting with general ideas 

 in the mind. That this is possible depends in great part on the use 

 of symbols, such as notations, graphs, visual images, and most 

 familiarly, of course, words. That intellectual experiments may 

 continue in dreams is well known; and there are many instances of 

 effective unconscious cerebration, when the solution of a problem 

 appears without deliberate effort. We attach importance to this, 

 because there is reason to believe, as we shall see, that every level 

 of activity has a tendency towards some measure of enregistration 

 or automatisation. 



(II) INTELLIGENT BEHAVIOUR.— The next level is that of 

 intelligent behaviour, which cannot be adequately described apart 

 from perceptual inference. There is evidence of some understanding 

 of the situation, some perception of relations, some adjustment of 

 old means to new ends, some degree of judgment. Much of man's 

 activity is on the intelligent plane, and the same is true of many 

 of the doings of the higher mammals, such as anthropoid apes, 

 horses, dogs, and elephants. At lower levels among vertebrate 

 animals it is more sporadic, being mingled with what is predomi- 

 nantly instinctive. Among Invertebrates it is rare, though it may 

 occasionally intervene in the marvellous routine of instinct. We are, 

 of course, using the term "instinct" in a precise way, to denote an 

 inborn or hereditary capacity for doing apparently clever things 

 without any need for apprenticeship; and the student will imder- 

 stand that some of the instinctive achievements of ants and bees 

 are at a much higher level of intricacy and effectiveness than a 

 simple intelligent action on the part of a mammal. But they are on 

 a different line of evolution. 



Intelligence of Apes. — At this point some account must be 

 given of the recent studies on the behaviour of the higher apes — 

 studies which differ from most of the older ones in three ways: 

 that expert psychologists, accustomed to detect the pitfalls of 

 ijiterprctation, have taken a leading part in the inquiry; that care 

 has been taken to supplement observation with experiment; and 



